Curable resin composition for overcoat of flexible circuit

ABSTRACT

Herein is desclosed a curable resin composition comprising at least one polyol selected from the group consisting of Polyol A, including polybutadiene polyol (Polyol Aa), Polyol B, including polybutadiene polyol (Polyol Ba) and polyester polyol (Polyol Bb), and Polyol C, and at least one polyblock isocyanate selected form the group consisting of polyblock isocyanate (Isocyanate X), including polybutadiene polyblock isocyanate (Isocyanate Xa), which is excellent in warp property, i.e., provides a low shrinkage, upon curing, and the cured products of which are particularly excellent in flexibility and excellent in such properties chemical resistance, heat resistance, electric insulation, bending resistance and adherence, and which is, therefore, suitable for overcoat of flexible circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to thermosetting resin compositions for overcoatsof flexible circuits, which are particularly excellent in low shrinkageduring curing and flexibility.

2. Prior Art

Formerly, the surface protective films of flexible wiring circuitsinclude, for example, those prepared by cutting polyimide films, calledas coverlay films, using a die made corresponding to the pattern, whichare then adhered onto a substrate with an adhesive; and those preparedby applying a ultraviolet rays--curable or thermosetting overcoatcomposition the film from which is imparted with flexibility, accordingto the screen printing method, the latter being more advantageous inworkability.

As such curable overcoats, resin compositions mainly consisting of anepoxy resin, an acryl resin, or a mixture thereof have been known. Theseresins often comprise, as main ingredients, a resin denatured byintroducing, particularly, a butadiene or siloxane skeleton, or a longchain fatty skeleton, thereby improving flexibility and preventing warpdue to cure shrinkage while trying to avoid reduction of inherent heatresistance, chemical resistance, and electrical insulation.

Recently, however, with lightening and miniaturization of electronicequipment (cameras, 8 mm automatic projectors, portable telephones,personal computers, printers, etc.), flexible substrates have beenreduced in thickness and weight, and thus more remarkably affected byflexibility and cure shrinkage of the cured resin composition to beovercoated. Therefore, curing type overcoats do not satisfy requirementsfor warp upon cure shrinkage and flexibility of the cured products.

[Problems to be Solved by the Invention]

In consideration of such points, there have been found no curable resincompositions having properties required of overcoats for flexiblecircuit such as low shrinkage during curing, and whose cured productshave satisfactory properties such as flexibility, adherence, electricalinsulation, chemical resistance, heat resistance, etc., and thereforedevelopment of such compositions has been expected.

SUMMARY OF THE INVENTION

The present inventors have studied intensively to solve the aboveproblems. As the results, they have attained a group of inventions solinked as to form a single general inventive concept.

A first one of the group of inventions relates to a curable resincomposition for overcoat of flexible circuit which comprises a polyolwith a number-average molecular weight of 1,000-8,000 and having 2-10hydroxyl groups per molecule, said polyol being sometimes referred to as"Polyol A" herein, and a polyblock isocyanate, said isocyanate beingsometimes referred to as "Isocyanate X" herein; and a curable resincomposition for overcoat of flexible circuit which comprises apolybutadiene polyol with a number-average molecular weight of1,000-8,000 and having 2-10 hydroxyl groups per molecule, said polyolbeing sometimes referred to as "Polyol Aa" herein, and polybutadienepolyblock isocyanate with a number-average molecular weight of1,000-8,000 and having 2-10 blockisocyanate groups per molecule, saidisocyanate being sometimes referred to as "Isocyanate Xa" herein.

Said invention has been attained based on the findings by the presentinventors that curing a urethane resin composition containing, as themain ingredient, a polyol with a number-average molecular weight of1,000-8,000 and having 2-10 hydroxyl groups (Polyol A) and polyblockisocyanate (Isocyanate X) provides a low shrinkage upon curing, and thata protective film resulting from curing has such satisfactoryflexibility, adherence, electric insulation, chemical resistance, heatresistance, and the like properties.

A second one of the group of inventions relates to a curable resincomposition for overcoat of flexible circuit which comprises a polyolwith a number-average molecular weight of 1,000-8,000 and having 2-10hydroxyl groups per molecule (Polyol A), a polyol with a number-averagemolecular weight of 13,000-30,000 and having 2-10 hydroxyl groups permolecule, said polyol being sometimes referred to as "Polyol B" herein,and a polyblock isocyanate (Isocyanate X) as the essential ingredient,wherein the weight ratio (as solid content) of said two polyols is(Polyol A):(Polyol B)=40:60-90:10, and said polyblock isocyanate(Isocyanate X) is in an amount of 0.8-3.5 gram equivalents based on,i.e., per one gram equivalent of, the total hydroxyl groups of the twopolyols (Polyol A plus Polyol B); and a curable resin composition forovercoat of flexible circuit which comprises a polyol with anumber-average molecular weight of 200-600 and having 2-10 hydroxylgroups per molecule, said polyol being sometimes referred to as "PolyolC" herein, a polyol with a number-average molecular weight of13,000-30,000 and having 2-10 hydroxyl groups per molecule (Polyol B),and a polyblock isocyanate (Isocyanate X), wherein the weight ratio (assolid content) of the polyols is (Polyol C):(Polyol B)=20:80-50:50 andthe polyblock isocyanate (Isocyanate X) is in an amount of 0.8-3.5 gramequivalents based on the total hydroxyl groups of the polyols.

Said invention has been attained based on the findings by the presentinventors that mixing a polyol with a number-average molecular weight of1,000-8,000 and having 2-10 hydroxyl groups per molecule (Polyol A) or apolyol with a number-average molecular weight of 200-600 and having 2-10hydroxyl groups per molecule (Polyol C), and a polyol with anumber-average molecular weight of 13,000-30,000 and having 2-10hydroxyl groups per molecule (Polyol B), and a polyblock isocyanate(Isocyanate X) at a defined ratio provides a low shrinkage upon curingand that a protective film resulting from curing has such satisfactoryflexibility, adherence, electric insulation, chemical resistance, heatresistance, and the like properties.

And, a third one of the group of inventions relates to a curable resincomposition for overcoat of flexible circuit which comprises, as theessential ingredient, a polybutadiene polyol with a number-averagemolecular weight of 1,000-8,000 and having 2-10 hydroxyl groups permolecule (Polyol Aa), a polyester polyol with a number-average molecularweight of 13,000-30,000 and having 2-10 hydroxyl groups per molecule,said polyol being sometimes referred to as "Polyol Bb" herein, and apolybutadiene polyblock isocyanate with a number-average molecularweight of 1,000-8,000 and having 2-10 blockisocyanate groups permolecule (Isocyanate Xa), wherein the weight ratio of said polyols (assolid content) is (Polyol Aa):(Polyol Bb)=40:60-90:10 and said polyblockisocyanate (Isocyanate Xa) is in an amount of 0.8-3.5 gram equivalentsbased on the total hydroxyl groups of the polyols.

Said invention has been attained based on the findings by the presentinventors that mixing a polybutadiene polyol with a number-averagemolecular weight of 1,000-8,000 and having 2-10 hydroxyl groups permolecule (Polyol Aa) and a polyester polyol with a number-averagemolecular weight of 13,000-30,000 and having 2-10 hydroxyl groups permolecule (Polyol Bb), and a polybutadiene polyblock isocyanate with anumber-average molecular weight of 1,000-8,000 and having 2-10 hydroxylgroups per molecule (Isocyanate Xa) at a defined ratio provides a lowshrinkage upon curing and that a protective film resulting from curinghas such satisfactory flexibility, adherence, electrical insulation,chemical resistance, heat resistance, and the like properties.

DETAILED DESCRIPTION OF THE INVENTION

The group of inventions will be sequentially illustrated in detailbelow.

Firstly, the first invention will be illustrated in detail.

As for the ingredients of the present curable resin composition forflexible circuit overcoat, the ratio of a polyol with a number-averagemolecular weight of 1,000-8,000 and having 2-10 hydroxyl groups permolecule (Polyol A) to a polyblock isocyanate (Isocyanate X) ispreferably in an amount of 0.8-3.5 gram equivalents of the polyblockisocyanate based on, i.e., per one gram equivalent of, the hydroxylgroups of the polyol.

A polyol with a number-average molecular weight of 1,000-8,000 andhaving 2-10 hydroxyl groups per molecule is important to impartproperties to cured products, for example, those observed for rigidresins such as heat resistance, chemical resistance, and the like, aswell as those observed for flexible resins such as flexibility, lowshrinkage, and the like. When the molecular weight is below this rangeor when the number of hydroxyl groups per molecule exceeds this range,the crosslinking density upon curing becomes higher, providing hardercured products and insufficient properties for low shrinkage upon curingand flexibility of a cured film. On the other hand, when the molecularweight exceeds said range or when the number of hydroxyl groups permolecule is below said range, the crosslinking density upon curingbecomes lower, providing more flexible cured products whilesignificantly deteriorating heat resistance and chemical resistance ofthe cured film.

Any polyols with a number-average molecular weight of 1,000-8,000 andhaving 2-10 hydroxyl groups per molecule may be used as Polyol A,irrespective of the resin structure. Such polyols include, for example,acryl polyols prepared by copolymerization of a hydroxyl-groupcontaining olefin such as a vinyl alcohol or allyl alcohol with anotherolefin; polyester polyols and polyether polyols retaining terminalhydroxyl groups by altering molar ratio of polymerization; andpolybutadiene wherein hydroxyl groups are introduced upon denaturationof resin and hydroxyl-terminated polyolefins. Resins satisfying theabove requirements for molecular weight and number of hydroxyl groupsare all encompassed. Acryl polyols include "Desmofene A665"(manufactured by Sumitomo Bayer Urethane); polyester polyol (Polyol Bb),"HM-1" (manufactured by Arakawa Chemical Industry), "Eryether UE3320"(manufactured by Unitika Ltd.); hydroxyl group-containing polybutadiene(Polyol Aa), "G-1000", "GI-1000" and "GQ-1000" (manufactured by NipponSoda Co., Ltd.); hydroxyl-terminated polyolefins, "Polyether-H"(manufactured by Mitsubishi Chemical Corp.). Among them, hydroxylgroup-containing polybutadienes (Polyol Aa) are preferably used toimpart flexibility.

Polyblock isocyanates (Isocyanate X) with a number-average molecularweight of 1,000-8,000 and having 2-10 block isocyanate groups permolecule are important to provide the cured products with both theproperties of rigid resins such as heat resistance, chemical resistance,etc. and those of flexible resins such as flexibility, low shrinkage,etc. Where the molecular weight is below said range, or where the numberof hydroxyl groups per molecule is above said range, the crosslinkingdensity upon curing becomes higher, providing harder cured products.Therefore, properties satisfactory for flexibility of cured films or lowshrinkage upon curing can not be obtained. On the other hand, where themolecular weight is above said range, or where the number of hydroxylgroups per molecule is below said range, the crosslinking density uponcuring becomes lower, resulting in more flexible cured products, whileheat resistance and chemical resistance of the cured film beingremarkably deteriorated. Further, where such components (Polyol X) arethose having polybutadiene skeletons (Polyol Xa), they serve to improvelow shrinkage upon curing and flexibility.

Polyblock isocyanates (Isocyanate X) may be obtained by blockingpolyisocyanate having two or more functional groups with a blockingagent. Such polyisocyanates include, for example, diisocyanates such astoluene-2,4-diisocyanate, toluene-2,6-diisocyanate, hexamethylenediisocyanate, xylylene diisocyanate, diphenyl methane diisocyanate,isophorone diisocyanate; those having three or more functional groupsprepared from the above diisocyanates utilizing cyclization andtrimerization of isocyanate groups; and those having three or morefunctional groups prepared by partly reacting isocyanate groups withvarious polyols. Blocking agents include, for example, a compound havingonly one active hydrogen atom which can react with an isocyanate group,per molecule and preferably dissociates again at a temperature below170° C. after reaction with the isocyanate group, and include, forexample, ε-caprolactam, diethyl malonate, ethyl acetoacetate, acetoxime,methylethylketoxime, phenol, cresol, etc.

Among them, in order to improve low shrinkage during curing andflexibility, polyisocyanates having butadiene skeletons in theirmolecules and blocked with the above blocking agents (Isocyanate Xa) arepreferred, and include, for example, "TP-1002" (manufactured by NipponSoda Co., Ltd.), "HTP-9", "HTP-5MLD" and "Unimax P" (manufactured byIdemitsu Petrochemical).

Moreover, the present composition may optionally comprise a curingaccelerator for polyol and isocyanate, a filler, an additive, athixotropic agent, a solvent and the like as optional components, inaddition to the above essential components. Particularly, in order toimprove bending resistance, fine rubber particles may be preferablyadded. Moreover, fine polyamide particles may be added to furtherimprove adherence to a base copper circuit, a base material such as apolyimide or polyester film, an adhesive layer, etc.

Such fine rubber particles include, for example, any fine particles ofresins exhibiting rubber elasticity such as acrylonitrile butadienerubber, butadiene rubber, acryl rubber, which have been subjected tochemical crosslinking treatment to make insoluble in an organic solventand infusible. For example, "XER-91" (manufactured by Japan SyntheticRubber Co., Ltd.), "Staphyloide AC3355", "Staphyloide AC3832" and"IM101" (manufactured by Takeda Chemical Industries, Ltd.), "ParaloideEXL2655" and "Paraloide EXL2602" (manufactured by Kureha ChemicalIndustries, Co., Ltd.) are encompassed.

Fine polyamide particles include any fine particles of 50 micron orsmaller consisting of resin having amide linkages, for example, fattypolyamides such as nylon, aromatic polyamides such as Kevlar, andpolyamidoimides. For example, "VESTOSINT 2070" (manufactured by DaicelHuls) and "SP500" (manufactured by Toray Industries, Inc.) may bementioned.

The method of curing the curable resin composition of the presentinvention in itself is not particularly limited, but carried outaccording to the conventional methods.

Now, the second invention will be illustrated in detail.

The effect of polyols with a number-average molecular weight of1,000-8,000 and having 2-10 hydroxyl groups per molecule (Polyol A) onthe physical properties of the cured product of the curable resincomposition of the present invention is same as that explained inrelation to the first invention.

A polyol with a number-average molecular weight of 200-600 and having2-10 hydroxyl groups per molecule (Polyol C) is a component to impartproperties inherent to rigid cured materials such as heat resistance andchemical resistance to the cured products of the curable resincomposition of the present invention, and serves to increase thecrosslinking density upon curing. On the other hand, a polyol with anumber-average molecular weight of 13,000-30,000 and having 2-10hydroxyl groups per molecule is important to impart properties inherentto flexible cured materials such as improved low shrinkage upon curingand flexibility of the cured products.

When Polyol C is solely cured using polyisocyanate, the crosslinkingdensity becomes relatively higher, resulting in insufficient lowshrinkage upon curing and insufficient flexibility of the coat film. Onthe other hand, when Polyol B is solely cured using polyisocyanate, thecrosslinking density is remarkably reduced, resulting in remarkablydeteriorated properties of the coat film such as heat resistance andchemical resistance. To obtain satisfactory low shrinkage upon curing,and comply with flexibility, heat resistance, and chemical resistance ofthe coat film, it is necessary to mix two types of polyols havingdifferent properties at a certain ratio. That is, it is preferable touse two polyols mixed at the ratio, i.e., (Polyol C):(PolyolB)=20:80-50:50. When the amount of Polyol C is less than this range, thecrosslinking density excessively decreases, resulting in remarkablydeteriorated properties of the coat film such as heat resistance, andchemical resistance. On the other hand, when the amount of Polyol C isgreater, the crosslinking density excessively increases, resulting indeteriorated low shrinkage upon curing and decreased flexibility of thecoat film.

On the other hand, when Polyol A is solely cured using polyisocyanate,the cured product thus obtained is relatively balanced in suchproperties as low shrinkage upon curing, and heat resistance, chemicalresistance and flexibility, but the low shrinkage upon curing andflexibility are not completely satisfactory. Therefore, it is necessaryto use Polyol A in combination with Polyol B. That is, it is preferableto use them by mixing within the range, (Polyol A):(PolyolB)=40:60-90:10. When the amount of Polyol A is smaller than this range,the crosslinking density is excessively reduced, resulting in remarkablydeteriorated properties such as heat resistance, and chemical resistanceof the coat film.

Polyol A, including Polyol Aa, is the same as those previously explainedin relation to the first invention.

Polyol B may be any polyol with a number-average molecular weight of13,000-30,000 and having 2-10 hydroxyl groups per molecule, irrespectiveof the resin structure, and include those satisfying the aboverequirements for molecular weight and number of hydroxyl groups, forexample, acryl polyols prepared by copolymerization of a hydroxylgroup-containing olefin such as a vinyl alcohol or allyl alcohol withanother olefin; polyester polyol (Polyol Bb) or polyether polyolretaining terminal hydroxyl groups by altering molar ratio duringpolymerization; as well as polybutadiene prepared by introducinghydroxyl groups by denaturing the resin (Polyol Ba), hydroxyl-terminatedpolyolefin, etc.

Such acryl polyols include, for example, "Desmophene A450" (manufacturedby Sumitomo Bayer Urethane); polyester polyols include, for example,"Bilon-200" (manufactured by Toyobo Co., Ltd.), "Eryether UE3600"(manufactured by Unitika Ltd.), as well as a hydroxyl group-containingpolyisoprene, "LIR506" (manufactured by Kuraray Co., Ltd.), and theabove Polyol A wherein the hydroxyl groups have been partly crosslinkedto polymerize using polyisocyanate, polycarboxylic acid, polyacidanhydride, or the like. Among them, in order to impart more flexibility,hydroxyl group-containing polybutadienes with a molecular weight of1,000-8,000 (Polyol Aa), wherein the hydroxyl groups have been partlycrosslinked using polyisocyanate, polycarboxylic acid, polyacidanhydride or the like, are preferred.

Polyol C includes those polyols with a number-average molecular weightof 200-600 and having 2-10 hydroxyl groups per molecule, irrespective ofthe resin structure. For example, EO denatured pentaerythritol, "PE555"(manufactured by Toho Chemical Industries Co., Ltd.), EO denaturedtrimethyrol propane, "TP880" (manufactured by Toho Chemical IndustriesCo., Ltd.), and polycaprolactone triol, "Prakcel303", and "Prakcel 305"(manufactured by Daicel Huls).

Polyblock isocyanates (Isocyanate X), including polybutadiene polyblockisocyanates (Isocyanate Xa), are the same as described above for thefirst invention.

Optional ingredients, in addition to the above essential ones, may beadded as needed or optionally to the present composition. Suchingredients are the same as described above for the first invention.

The method of curing the present curable resin composition in itself isnot particularly limited, but carried out according to the conventionalmethods.

Finally, the third invention will be illustrated in detail.

Effects of polybutadiene polyols with a number-average molecular weightof 1,000-8,000 and having 2-10 hydroxyl groups per molecule (Polyol Aa)on the physical properties of the cured products of the curable resincomposition of the present inveintion is the same as those of Polyol Aexplained above for the first invention. Such polybutadienes (PolyolAa), due to their polybutadiene skeletons, have effect to improve lowshrinkage upon curing of the resin composition of the present inventionand the flexibility of the cured resin composition, i.e., the curedproduct.

Polyester polyols with a number-average molecular weight of13,000-30,000 and having 2-10 hydroxyl groups per molecule (Polyol Bb)are important to provide properties inherent to flexible cured materialssuch as low shrinkage upon curing, increased flexibility and the like,as well as to improve adherence to base materials due to effect ofhighly polar ester linkage contained in the resin skeletons.

The effects of block isocyanates (Isocyanate X), including polybutadienepolyblock isocyanate (Isocyanate Xa), on the cured product from thecurable resin composition of the present invention is same as thoseexplained above for the first invention.

When a polybutadiene polyol (Polyol Aa) is solely cured with apolybutadiene polyisocyanate (Isocyanate Xa), the resulting curedmaterial is relatively balanced in such properties as low shrinkage uponcuring, and heat resistance, chemical resistance, and flexibility; butthe low shrinkage upon curing, and flexibility, and adherence to basematerial are insufficient. Therefore, it is necessary to use Polyol Aain combination with polyester polyol (Polyol Bb). That is, it ispreferable to use them by mixing at a ratio (Polyol Aa):(PolyolBb)=40:60-90:10. When the amount of Polyol Aa is smaller than thisrange, the crosslinking density is excessively reduced, resulting inremarkably deteriorated properties such as heat resistance, chemicalresistance and the like of the coat film. A polybutadiene polyblockisocyanate (Isocyanate Xa) is preferably in an amount of 0.8-3.5 gramequivalents based on the total hydroxyl groups of the polyol. Thesmaller or greater amount compared with the said range results inexcessively reduced crosslinking density, providing remarkablydeteriorated properties such as heat resistance, chemical resistance andthe like of the coat film.

As polybutadiene polyols (Polyol Aa), any polyol with a number-averagemolecular weight of 1,000-8,000 and having 2-10 hydroxyl groups permolecule and a butadiene skeleton, may be used. For example, "G-1000","GI-1000" and "GQ-1000" (manufactured by Nippon Soda Co., Ltd.), and"R-45EPI" (manufactured by Idemitsu Petrochemical) may be mentioned.

As polyester polyols (Polyol Bb), any polyol with a number-averagemolecular weight of 13,000-30,000 and having 2-10 hydroxyl groups permolecule as well as polyester skeleton may be used. For example,"Bilon-200", "Bilon-103" and "Bilon-600" (manufactured by Toyobo Co.,Ltd.), "Eryether UE3400", "Eryether UE3500" and "Eryether UE3600"(manufactured by Unitika Ltd.), "Aronmelt PES310-S30", "AronmeltPES340-S30" and "Aronmelt PES390-S30" (manufactured by Toagosei Co.,Ltd.) are included.

Polybutadiene polyblock isocyanates (Isocynate Xa) are those obtained byblocking isocyanate-containing polybutadiene polyisocyanate with ablocking agent. Such polybutadiene polyisocyanates include, for example,diisocyanates such as toluene-2,4-diisocyanate,toluene-2,6-diisocyanate, hexamethylene diisocyanate, xylylenediisocyanate, diphenyl methane diisocyanate, and isophoronediisocyanate; the above diisocyanates which have been made to have threeor more functional groups utilizing cyclization and trimerization of theisocyanate groups; and those prepared by reacting a diisocyanate whichhas been made to have three or more functional groups by partly reactingthe isocyanate groups with various polyols, with a hydroxylgroup-containing polybutadiene having a number-average molecular weightof 600-7,000. Isocyanate Xa includes, for example "TP-1002"(manufactured by Nippon Soda Co., Ltd.), and "HTP-9", "HTP-5MLD" and"Unimax P" (manufactured by Idemitsu Petrochemical). Blocking agentsinclude, for example, a compound having only one active hydrogen atomwhich is able to react with an isocyanate group, per molecule andpreferably dissociates again at a temperature not higher than 170° C.after reaction with the isocyanate group, and include, for example,ε-caprolactam, diethyl malonate, ethyl acetoacetate, acetoxime,methylethylketoxime, phenol, cresol, etc.

The composition of the present invention may be compounded with optionalingredients in addition to the above essential ones as needed oroptionally. Such optional ingredients are the same as those described inrelation to the first invention.

The method of curing the curable resin composition of the presentinvention in itself is not particularly limited, and carried outaccording to the conventional methods.

The group of inventions so linked as to form a single general inventiveconcept are explained classifying into three types of inventions.However, such explanation is made just to facilitate understanding. Acurable resin composition which contains at least one polyol selectedfrom the group consisting of Polyol A, including polybutadiene polyol(Polyol Aa), Polyol B, including polybutadiene polyol (Polyol Ba) andpolyester polyol (Polyol Bb), and Polyol C, and at least one polyblockisocyanate selected form the group consisting of polyblock isocyanate(Isocyanate X), including polybutadiene polyblock isocyanate (IsocyanateXa), and which provides cured products (coat film) having the sameproperties as those of the above described curable resin compositions ofthe first to third 0inventions are encompassed in the present invention.

EXAMPLES

The production examples of polyols and block isocyanates to be used inthe present invention and examples of the present invention as well ascomparative examples will be described to further explain the presentinvention.

(a) Production Examples of Resins Used in Examples and ComparativeExamples

<Production of Resin varnish E>

"Bilon-200" (OH terminated polyester, Mn=ca. 15,000, OH equivalent=7,014g/eq., and solid content=100 wt %: manufactured by Toyobo Co., Ltd.)(2,250 g), ethyl diglycol acetate (manufactured by Daicel ChemicalIndustries, Ltd.) (1,833 g), and "Ipsol150" (manufactured by IdemitsuPetrochemical) (917 g) were charged in a reactor, and stirred whileheating at 130° C. to dissolve to obtain a resin varnish. The productwill be called Resin varnish E.

Properties of Resin varnish E: Mn=ca. 15,000, OH equivalent (includingthe solvent)=15,586 g/eq., and solid content=45 wt %.

<Production of Resin varnish F>

"HTP-9" (NCO terminated polybutadiene, Mn=ca. 2,800, NCO equivalent=467g/eq., and solid content=100 wt %: manufactured by IdemitsuPetrochemical) (1,000 g), ethyl diglycol acetate (manufactured by DaicelChemical Industries, Ltd.) (216 g) and dibutyltin laurate (0.1 g) werecharged in a reactor, and mixed to be homogeneously dissolved. Once themixture became homogeneous, it was raised in temperature to 70° C. andfurther stirred while methylethylketoxime (molecular weight, 87.12) (224g) was added dropwise with stirring over a period of 2 hours. Themixture was kept at the same temperature for an additional hour, andcooled at the time when FT-IR indicated disappearance of the NCO peak at2,250 cm⁻¹, to obtain a resin varnish. The product will be called Resinvarnish F.

Properties of Resin varnish F: Mn=ca. 2,800, NCO equivalent(includingthe solvent)=672.5 g/eq., and solid content=85 wt %.

<Production of Resin varnish G>

"G-1000" (OH terminated polybutadiene, Mn=ca 1,600, OH equivalent=801g/eq., solid content=100 w %: manufactured by Nippon Soda Co., Ltd.)(1,000 g), "Ipsol150" (manufactured by Idemitsu Petrochemical) (591 g)and dibutyltin laurate (0.1 g) were charged in a reactor, mixed andhomogeneously dissolved. The mixture was raised in temperature to 70° C.at the time when the mixture became homogeneous and further stirredwhile toluene-2,4-diisocyanate (NCO equivalent=87.08 g/eq.) (97.8 g) wasadded dropwise with stirring over a period of 2 hours. The mixture waskept at the same temperature for an additional hour, and cooled at thetime when FT-IR indicated disappearance of the NCO peak at 2,250 cm⁻¹,to obtain a resin varnish. The thus obtained resin varnish will becalled Resin varnish G.

Properties of Resin varnish G: Mn=ca. 17,000, OH equivalent (includingthe solvent)=13,532 g/eq., and solid content=65%.

(b) Details of the Individual Ingredients Used in Examples andComparative Examples

<Polyol A>

"Desmophene A665" (acryl polyol, Mn=ca. 1,000, OH equivalent (includingthe solvent)=607 g/eq., and solid content=65 wt %: manufactured bySumitomo Bayer Urethane)

"G-1000" (polybutadiene polyol, being also a Polyol Aa, Mn=ca. 1,500, OHequivalent=801 g/eq., and solid content=100 wt %: manufactured by NipponSoda Co., Ltd.)

<Polyol B>

"LIR506" (polyisoprene polyol, Mn=ca. 25,000, OH equivalent=4,237 g/eq.,and solid content=100 wt % manufactured by Kuraray Co., Ltd.)

Resin varnish G (polybutadiene polyol, being also a Polyol Ba, Mn=ca.17,000, OH equivalent (including the solvent)=13,532 g/eq., and solidcontent=65 wt %)

Resin varnish E (polyester polyol, being also a Polyol Bb, Mn=ca.15,000, OH equivalent (including the solvent)=15,586 g/eq., and solidcontent=45 wt %)

<Polyol C>

"PE555" (EO denatured pentaerythritol, Mn=ca. 550, OH equivalent=138g/eq., and solid content=100 wt %: manufactured by Toho ChemicalIndustries Co., Ltd.)

<Polyblock isocyanate X>

"BL4265" (oxime block isocyanate of isophorone diisocyanate trimer, NCOequivalent (including the solvent)=519 g/eq., and solid content=65 wt %:manufactured by Sumitomo Bayer Urethane)

Resin varnish F (polybutadiene polyblockisocyanate, being also aIsocyanate Xa, Mn=ca. 2,800, NCO equivalent (including thesolvent)=672.5 g/eq., and solid content=85 wt %)

(c) Measurement of the Properties of Coat Film

(1) Warp upon cure shrinkage: Sample is coated (25 mm×35 mm×25 μm) on apolyimide film (35 mm×60 mm×75 μm), and the degree of warp after curingis measured.

(2a) Anti-bending test (1): Mandrel test; Bending test is carried out bybending within the range from 1 to 1/8 inches diameter. The result isexpressed as a minimum diameter generating no crack.

(2b) Anti-bending test (2): This test is carried out according to JISD0202. The diameter of the bent section is 0.38 mm. The number ofrepetition of bending before the sample is cracked is measured. Theresults are expressed as X: less than 10, Δ: 10-1,000, ◯: 1,000-2,000,and ⊚: more than 2,000.

(3) Pencil hardness test: According to JIS D0202.

(4) Electric insulation: Sample is coated on a tandem electrode(conductor width, 0.318 mm), and electric resistance after boiling foran hour is measured.

(5) Chemical resistance: A paint coat is rubbed with a waste soaked withacetone or isopropanol. The results are expressed as ◯: nothing abnormalobserved, and X: coating deteriorated.

(6) Heat resistance upon soldering: Flux JS-64MS-S is coated onto apaint coat, which is soaked in a soldering bath at 260° C. for 10seconds. The results are expressed as ◯: nothing abnormal observed, andX: blister generated.

(7) Adherence: According to JIS D0202, the test is carried out oncopper, polyimide "Yupilex S" manufactured by Ube-Kosan Co., Ltd., andthe adhesive layer of flexible substrate as base materials. The resultsare expressed as X: 0/100-50/100, Δ: 51/100-99/100, and ◯: 100/100.

(d) Preparation and Curing of Curable Resin Compositions

The above polyols, polyblock isocyanates, fine rubber particles and finepolyamide particles were properly compounded in such ratios as shown inthe following Table 1. Then, as other ingredients, dibutyltin laurate asa curing accelerator, "Aerosil200" (manufactured by Nihon Aerosil) as ananti-sagging agent, and carbitol acetate as a viscosity adjuster wereadded in appropriate amounts for each case and mixed, followed bykneading using a three roll mill to prepare curable resin compositionsamples A1-A9 corresponding to Examples 1-9, respectively. The thusprepared samples A1-A9 were each coated on bases in about 25 μmthickness, and cured under the conditions of 150° C. for 60 minutes, toprepare test samples of cured products. Incidentally, in the table,Examples 1-2 (Samples A1-A2) are embodiments of the first invention,Examples 3-6 (Samples A3-A6), of the second invention, and Example 7(Sample A7), of the third invention.

The products were measured according to the above method for measurementof the properties of coat film given under (c) above. The results areshown in the Table 2 below.

                                      TABLE 1                                     __________________________________________________________________________                     Examples                                                                      1  2  3 4 5  6  7 8 9                                        Samples          A1 A2 A3                                                                              A4                                                                              A5 A6 A7                                                                              A8                                                                              A9                                       __________________________________________________________________________    Polyol A: "Desmophene A665"                                                                    10    9.2                                                    Polyol Aa: "G-1000" 10   6       6 6 6                                        Polyol B: "LIR506"     4   6                                                  Polyol Ba: Resin varnish G                                                                             6.2  9.2                                             Polyol Bb: Resin varnish E       8.9                                                                             8.9                                                                             8.9                                      Polyol C: "PE555"          4  4                                               Polyisocyanate X: "BL4265"                                                                     8.6   8.4 15.8                                               Polyisocyanate Xa: Resin varnish F                                                                8.4  5.4  20 5.5                                                                             5.5                                                                             5.5                                      Fine rubber particle: "XER-91"       2                                        Fine polyamide particle: "VENTSINT"                                                                              1 1                                        __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________                 Examples                                                                      1   2   3   4   5   6   7   8   9                                Samples      A1  A2  A3  A4  A5  A6  A7  A8  A9                               __________________________________________________________________________    Wrap (mm)    1.2 0.8 0.7 0.5 0.7 0.5 0.4 0.4 0.3                              Anti-bending test(1) Mandrel                                                               1/8>                                                                              1/8>                                                                              1/8>                                                                              1/8>                                                                              1/8>                                                                              1/8>                                                                              1/8>                                                                              1/8>                                                                              1/8>                             Anti-bending test(2)                                                                       ◯                                                                     ◯                                                                     ◯                                                                     ⊚                                                                  ◯                                                                     ⊚                                                                  ⊚                                                                  ⊚                                                                  ⊚                 Pencil hardness                                                                            4H  3H  3H  2H  3H  2H  2H  2H  2H                               Electric insulation(Ω)                                                               10th                                                                              10th                                                                              10th                                                                              10th                                                                              10th                                                                              10th                                                                              10th                                                                              10th                                                                              10th                                          power                                                                             power                                                                             power                                                                             power                                                                             power                                                                             power                                                                             power                                                                             power                                                                             power                            Chemical resistance:                                                          Acetone      ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                    Isopropanol  ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                    Heat resistance upon soldering                                                             ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                    Adherence onto:                                                               Copper       ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                    Polyimide    Δ                                                                           ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                    Adhesive layer of                                                                          ◯                                                                     Δ                                                                           ◯                                                                     Δ                                                                           ◯                                                                     Δ                                                                           ◯                                                                     ⊚                                                                  ⊚                 Flexible substrate                                                            __________________________________________________________________________

As in the Examples, Samples B1-B4 of Comparative Examples 1-4,respectively, were prepared using the compositions shown in thefollowing Table 3, and evaluated in the same manner as in the aboveExamples. The results are shown in Table 4 below.

                  TABLE 3                                                         ______________________________________                                                        Comparative Examples                                                          1    2        3     4                                         Samples           B1     B2       B3  B4                                      ______________________________________                                        Polyol A: "Desmophene A665"       4.6                                         Polyol B: "LIR506"       10       7   3                                       Polyol C: "PE555" 10                  7                                       Polyisocyanate X: "BL4265"                                                                      37.6   1.2      4.8 26.7                                    ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                                      Comparative Examples                                                          1     2        3       4                                        Samples         B1      B2       B3    B4                                     ______________________________________                                        Wrap (mm)       9.0     0.5      0.5   5.0                                    Anti-bending test (1) Mandrel                                                                 1<      1/8>     1/8>  1<                                     Anti-bending test (2)                                                                         x       ∘                                                                          ∘                                                                       x                                      Pencil hardness 4H      F        F     4H                                     Electric insulation (Ω)                                                                 10th    8th      9th   10th                                                   power   power    power power                                  Chemical resistance:                                                          Acetone         ∘                                                                         x        x     ∘                          Isopropanol     ∘                                                                         ∘                                                                          ∘                                                                       ∘                          Heat resistance upon soldering                                                                ∘                                                                         x        x     ∘                          Adherence onto:                                                               Copper          x       ∘                                                                          ∘                                                                       x                                      Polyimide       x       x        x     x                                      Adhesive layer of                                                                             x       x        x     x                                      Flexible substrate                                                            ______________________________________                                    

As has been described above, curable resin compositions of the presentinvention are, compared with the conventional curable resincompositions, excellent in warp property upon curing, and the curedproducts thereof are particularly excellent in flexibility and excellentin such properties chemical resistance, heat resistance, electricinsulation, bending resistance and adherence. For these reasons, curableresin compositions of the present invention are suitable for overcoat offlexible circuit.

What is claimed is:
 1. A curable resin composition for overcoat offlexible circuit which comprises a polyol with a number-averagemolecular weight of 1,000-8,000 and having 2-10 hydroxyl groups permolecule (Polyol A), a polyol with a number-average molecular weight of13,000-30,000 and having 2-10 hydroxyl groups per molecule (Polyol B),and a blocked polyisocyanate (Isocyanate X) as the essential ingredient,wherein the weight ratio (as solid content) of said two polyols is(Polyol A):(Polyol B)=40:60-90:10, and said blocked polyisocyanate(Isocyanate X) is in an amount of 0.8-3.5 gram equivalents based on thetotal hydroxyl groups of the two polyols (Polyol A plus Polyol B),wherein said Polyol A is a polybutadiene polyol with a number-averagemolecular weight of 1,000-8,000 and having 2-10 hydroxyl groups permolecule (Polyol Aa), said Polyol B is a polybutadiene polyol with anumber-average molecular weight of 13,000-30,000 and having 2-10hydroxyl groups per molecule (Polyol Ba), and said Isocyanate X is apolybutadiene blocked polyisocyanate with a number-average molecularweight of 1,000-8,000 and having 2-10 blocked isocyanate groups permolecule (Isocyanate Xa), and wherein the weight ratio (as solidcontent) of said two polyols is (Polyol Aa):(Polyol Ba)=40:60-90:10, andsaid blocked polyisocyanate (Isocyanate Xa) is in an amount of 0.8-3.5gram equivalents based on the total hydroxyl groups of the two polyols(Polyol Aa plus Polyol Ba).
 2. A curable resin composition for overcoatof flexible circuit which comprises a polyol with a number-averagemolecular weight of 200-600 and having 2-10 hydroxyl groups per molecule(Polyol C), a polyol with a number-average molecular weight of13,000-30,000 and having 2-10 hydroxyl groups per molecule (Polyol B),and a blocked polyisocyanate (Isocyanate X), wherein the weight ratio(as solid content) of the polyols is (Polyol C):(Polyol B)=20:80-50:50and the blocked polyisocyanate (Isocyanate X) is in an amount of 0.8-3.5gram equivalents based on the total hydroxyl groups of the polyols,wherein said Polyol B is a polybutadiene polyol with a number-averagemolecular weight of 13,000-30,000 and having 2-10 hydroxyl groups permolecule (Polyol Ba), and said Isocyanate X is a polybutadiene blockedpolyisocyanate with a number-average molecular weight of 1,000-8,000 andhaving 2-10 blocked isocyanate groups per molecule (Isocyanate Xa).
 3. Acurable resin composition for overcoat of flexible circuit whichcomprises, as the essential ingredient, a polybutadiene polyol with anumber-average molecular weight of 1,000-8,000 and having 2-10 hydroxylgroups per molecule (Polyol Aa), a polyester polyol with anumber-average molecular weight of 13,000-30,000 and having 2-10hydroxyl groups per molecule (Polyol Bb), and a polybutadiene blockedpolyisocyanate with a number-average molecular weight of 1,000-8,000 andhaving 2-10 blocked isocyanate groups per molecule (Isocyanate Xa),wherein the weight ratio of said polyols (as solid content) is (PolyolAa):(Polyol Bb)=40:60-90:10 and said blocked polyisocyanate (IsocyanateXa) is in an amount of 0.8-3.5 gram equivalents based on the totalhydroxyl groups of the polyols.
 4. The curable resin composition forovercoat of flexible circuit as set forth in claim 1 which furthercomprises fine rubber particles and/or fine polyamide particles.
 5. Thecurable resin composition for overcoat of flexible circuit as set forthin claim 2 which further comprises fine rubber particles and/or finepolyamide particles.
 6. The curable resin composition for overcoat offlexible circuit as set forth in claim 3 which further comprises finerubber particles and/or fine polyamide particles.
 7. A cured product inthe shape of a thin membrane, resulting from curing of the curable resincomposition as set forth in claim
 1. 8. A cured product in the shape ofa thin membrane, resulting from curing of the curable resin compositionas set forth in claim
 2. 9. A cured product in the shape of a thinmembrane, resulting from curing of the curable resin composition as setforth in claim
 3. 10. A cured product in the shape of a thin membrane,resulting from curing of the curable resin composition as set forth inclaim
 4. 11. A cured product in the shape of a thin membrane, resultingfrom curing of the curable resin composition as set forth in claim 5.12. A cured product in the shape of a thin membrane, resulting fromcuring of the curable resin composition as set forth in claim 6.